如何通过在 forEach 循环中使用键返回我想要的对象？

Question

Consider this code:

const year = 1910;

const items = [
  {
    name: 'gallon of gas',
    year: 1910,
    price: .12
  },
  {
    name: 'gallon of gas',
    year: 1960,
    price: .30
  },
  {
    name: 'gallon of gas',
    year: 2010,
    price: 2.80
  }
]

How do I display the price of the object corresponding to the year defined above?

items.forEach(d => {
 if (d.year === year) {
   return d.price;
   }
});

^ Why doesn't that solution work?

Answer 1

The forEach() function doesn't return a value, regardless of what you return in the callback function. Use find() instead to find the item that matches your criteria:

 const year = '1910'; const items = [ { name: 'gallon of gas', year: 1910, price: .12 }, { name: 'gallon of gas', year: 1960, price: .30 }, { name: 'gallon of gas', year: 2010, price: 2.80 } ]; const item = items.find(i => i.year == year); console.log(item.price);

Note: you can't use strict comparison ( === ) in the callback to find() because you're comparing a year string to a year number . Probably a good idea to address that.

Answer 2

Because that return statement is inside of the handler of the function forEach , basically, you're returning the handler execution and not the main function.

What you need to do is either to use a for-loop or the function find as follow:

let found = items.find(d => d.year === year);
if (found) return found.price;

Or a vanilla for-loop:

for (let i = 0; i < items.length; i++) 
   if (items[i].year === year) return items[i].price;

Answer 3

This needs ES6 (babel). Hope this helps! Got it from https://zellwk.com/blog/looping-through-js-objects/ .

 const year = 1910; const items = [ { name: 'gallon of gas', year: 1910, price: .12 }, { name: 'gallon of gas', year: 1960, price: .30 }, { name: 'gallon of gas', year: 2010, price: 2.80 } ] const values = Object.values(items) for (const value of values) { //you can't return, but you can use the value or store it in a variable/array console.log(value.price); }